intro
Purpose:
- Preliminary look at hi/lo multivariate contrast (cross-validated euclidean) in each task.
- Preliminary qualitative comparison of effects of prewhitening and pattern standardization on multivariate contrast.
Notes on analyses:
Target TRs:
- Axcpt: 7, 8, 9
- Cuedts: 9, 10
- Stern: 11, 12
- Stroop: 2, 3, 4
Contrasts (cross-validated euclidean):
- Axcpt: \(\text{BY} - \text{BX}\)
- Cuedts: \((\text{InConSwitch} + \text{InConRepeat} - \text{ConSwitch} - \text{ConRepeat})/2\)
- Stern: \(\text{LL5RN} - \text{LL5NN}\)
- Stroop: \((\text{PC50InCon} + \text{biasInCon} - \text{PC50Con} - \text{biasCon})/2\)
Normalizations:
- “stand”: standardized cross-validated euclidean (comparable to linear correlation)
- the across-vertex mean and standard deviation are removed from patterns prior to cross-validation
- “unsta”: unstandardized cross-validated euclidean (includes mean and scale information)
- “white”: spatially pre-whitened cross-validated euclidean (‘mahalanobis’)
- using vertex-by-vertex inverse covariance matrix derived from residual timeseries
- “unwhite”: not spatially pre-whitened
Plotting and statistical details:
- within ‘curves’ sections, ribbons indicate 95% CI of bootstrapped mean beta across subjects (one ribbon per run).
- all p-value corrections were performed whole-cortex, with FDR.
- for “stats and maps” sections, HLM was used to estimate t-statistics on the hi-lo contrast per ROI:
- random-intercept models
- level-I: (TR within target window)*(run)
- level-2: subject
- \(\beta_{trs} = b_0 + x_{tr}b_1 + d_s + \epsilon_{trs}\)
- \(t, r, s\) are indices for TR, run, and subject
- \(x\) is dummy-coded predictor for hi condition; \(b_1\) reflects hi-lo contrast (fixed effect)
- \(d\) is is subject-specific intercept
- \(\epsilon\) is error
Network-level
Estimates are first averaged across parcels within network per subject. Group-level stats and plots are then displayed at the network-level.
curves
t-stats on contrast
parcel-level
curves
counts of significant effects per TR

maps (target TRs)
## $Axcpt
## [1] 260
##
## $Cuedts
## [1] 0
##
## $Stern
## [1] 0
##
## $Stroop
## [1] 490
Unthresholded and thresholded t-statistics displayed on inflated brains. Threshold at fdr-corrected p-value (across all parcels) of 0.05. Note: colors are reverse-scaled, i.e., dark == strong effect, light == weak effect (so strong effects show up on white background).